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Energies 2018, 11(2), 280; https://doi.org/10.3390/en11020280

Numerical Investigation on the Heat Extraction Capacity of Dual Horizontal Wells in Enhanced Geothermal Systems Based on the 3-D THM Model

1
School of Petroleum Engineering, China University of Petroleum (East China), Qingdao 266580, China
2
Evaluation and Detection Technology Laboratory of Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266100, China
3
Geotechnical Engineering Research Institute, Korea Institute of Civil Engineering and Building Technology, 283, Goyang-daero, Ilsanseo-gu, Goyang-si, Gyeonggi-do 10223, Korea
*
Authors to whom correspondence should be addressed.
Received: 29 November 2017 / Revised: 16 January 2018 / Accepted: 19 January 2018 / Published: 24 January 2018
(This article belongs to the Special Issue Geothermal Heating and Cooling)
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Abstract

The Enhanced Geothermal System (EGS) constructs an artificial thermal reservoir by hydraulic fracturing to extract heat economically from hot dry rock. As the core element of the EGS heat recovery process, mass and heat transfer of working fluid mainly occurs in fractures. Since the direction of the natural and induced fractures are generally perpendicular to the minimum principal stress in the formation, as an effective stimulation approach, horizontal well production could increase the contact area with the thermal reservoir significantly. In this paper, the thermal reservoir is developed by a dual horizontal well system and treated as a fractured porous medium composed of matrix rock and discrete fracture network. Using the local thermal non-equilibrium theory, a coupled THM mathematical model and an ideal 3D numerical model are established for the EGS heat extraction process. EGS heat extraction capacity is evaluated in the light of thermal recovery lifespan, average outlet temperature, heat production, electricity generation, energy efficiency and thermal recovery rate. The results show that with certain reservoir and production parameters, the heat production, electricity generation and thermal recovery lifespan can achieve the commercial goal of the dual horizontal well system, but the energy efficiency and overall thermal recovery rate are still at low levels. At last, this paper puts forward a series of optimizations to improve the heat extraction capacity, including production conditions and thermal reservoir construction design. View Full-Text
Keywords: enhanced geothermal system; THM coupling; horizontal well; heat extraction capacity; numerical simulation enhanced geothermal system; THM coupling; horizontal well; heat extraction capacity; numerical simulation
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Sun, Z.; Xin, Y.; Yao, J.; Zhang, K.; Zhuang, L.; Zhu, X.; Wang, T.; Jiang, C. Numerical Investigation on the Heat Extraction Capacity of Dual Horizontal Wells in Enhanced Geothermal Systems Based on the 3-D THM Model. Energies 2018, 11, 280.

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